title: Structural basis of cyanobacterial photosystem II Inhibition by the herbicide terbutryn.
abstract: Herbicides that target photosystem II (PSII) compete with the native electron acceptor plastoquinone for binding at the Q(B) site in the D1 subunit and thus block the electron transfer from Q(A) to Q(B). Here, we present the first crystal structure of PSII with a bound herbicide at a resolution of 3.2 Å. The crystallized PSII core complexes were isolated from the thermophilic cyanobacterium Thermosynechococcus elongatus. The used herbicide terbutryn is found to bind via at least two hydrogen bonds to the Q(B) site similar to photosynthetic reaction centers in anoxygenic purple bacteria. Herbicide binding to PSII is also discussed regarding the influence on the redox potential of Q(A), which is known to affect photoinhibition. We further identified a second and novel chloride position close to the water-oxidizing complex and in the vicinity of the chloride ion reported earlier (Guskov, A., Kern, J., Gabdulkhakov, A., Broser, M., Zouni, A., and Saenger, W. (2009) Nat. Struct. Mol. Biol. 16, 334-342). This discovery is discussed in the context of proton transfer to the lumen.
authors.affiliation: Institut für Chemie/Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Broser
authors.forename: Carina
authors.initials: C
authors.lastname: Glöckner
authors.forename: Azat
authors.initials: A
authors.lastname: Gabdulkhakov
authors.forename: Albert
authors.initials: A
authors.lastname: Guskov
authors.forename: Joachim
authors.initials: J
authors.lastname: Buchta
authors.forename: Jan
authors.initials: J
authors.lastname: Kern
authors.forename: Frank
authors.initials: F
authors.lastname: Müh
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
authors.forename: Wolfram
authors.initials: W
authors.lastname: Saenger
authors.forename: Athina
authors.initials: A
authors.lastname: Zouni
mesh_terms: D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000201:enzymology*; D006540:Herbicides / Q000737:chemistry* / Q000494:pharmacology; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D020836:Protein Structure, Quaternary; D013329:Structure-Activity Relationship; D014227:Triazines / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D006540:Herbicides; D045332:Photosystem II Protein Complex; D014227:Triazines; C010347:terbutryne